function noop() {}
function noop2() {
    return;
}

function noop3() {
    return undefined;
}

let obj: object;

function f1(a: any) {
    a.b(); // ok
}

function f2(a: unknown) {
    // a.b();
    // 对象的类型为 "unknown"
}

function fail(msg: string): never {
    throw new Error(msg);
}

function fn(x: string | number) {
    if (typeof x === 'string') {
        // do something
    } else if (typeof x === 'number') {
        // do something
    } else {
        x;
    }
}

function something(f: Function) {
    f(1, 2, 3);
}

export {};